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P75 nerve growth factor receptor (p75 NGF-R) is a low-affinity receptor expressed on the surface of neural crest-derived cells and in a variety of neural tumors. Strong p75 NGF-R expression has been found in spindle cell melanoma (SCM). We studied spindle cell neoplasms of sun-damaged skin to determine whether this marker can reliably distinguish between SCM and other spindle cell malignancies. We evaluated the staining of p75 NGF-R, S100, and HMB-45 in 11 cases of SCM, 16 cases of spindle cell squamous cell carcinoma (SCSCC), 19 cases of spindle cell atypical fibroxanthoma, 6 cases of cutaneous leiomyosarcoma, and 20 scars. Staining with p75 NGF-R was positive in all 11 of 11 (100%) cases of SCM, whereas S100 stained 10 of 11 (91%) cases, and HMB-45 was negative in all SCMs. In addition, there was superior intensity of the staining for p75 NGF-R in comparison to S100. P75-NGF-R showed focal positivity in 3 of 16 (19%) cases of SCSCC. None of the rest of the cases of SCSCC, and none of the cases of spindle cell atypical fibroxanthoma, cutaneous leiomyosarcoma, and scars expressed p75 NGF-R, S100, or HMB-45. P75 NGF-R is a useful marker to distinguish SCM from other spindle cell neoplasms of sun-damaged skin. This marker exhibits greater sensitivity than S100 in identifying SCM and may be a useful diagnostic and ancillary stain especially in the setting of an S100 negative spindle cell neoplasm.

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